|Publication number||US6936539 B2|
|Application number||US 10/671,186|
|Publication date||Aug 30, 2005|
|Filing date||Sep 24, 2003|
|Priority date||Sep 24, 2003|
|Also published as||US20050064718, US20060220184|
|Publication number||10671186, 671186, US 6936539 B2, US 6936539B2, US-B2-6936539, US6936539 B2, US6936539B2|
|Inventors||Zhiping Yin, Gurtej S. Sandhu|
|Original Assignee||Micron Technology, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (5), Non-Patent Citations (1), Referenced by (24), Classifications (35), Legal Events (9)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This invention relates to the field of semiconductor manufacture and, more particularly, to an antireflective coating for use during the manufacture of a semiconductor device, specifically during a photolithographic process.
During the formation of a semiconductor device such as memory devices, logic devices, microprocessors, etc., several photolithography steps are typically required. Each photolithography step includes the formation of a blanket photoresist (resist) layer, exposing portions of the resist layer to light using a mask or reticle, removing the exposed resist portions (or the unexposed resist portions if negative resist is used), etching the underlying layer using the resist as a pattern, then stripping the resist.
Many layers, for example some oxides and metals, have a highly polished surface which reflects light back to the photoresist and exposes the resist in unwanted areas. This unintentionally exposed portion of the photoresist is removed (or remains, in the case of negative resist) and results in less than desirable patterning of the underlying layer. One method used to decrease reflected light is through the use of dielectric antireflective coatings (DARC layers), which are well known in the art of photolithography. A DARC layer is formed as a blanket layer, typically from silicon-rich oxide or oxynitride using chemical vapor deposition (CVD), over the layer to be etched. The blanket resist layer is formed over the DARC layer, then exposed to a pattern of light projected through a reticle. The exposed portion of the resist (or the unexposed portion, if a negative resist is used) is removed. Next, the DARC layer and the underlying layer are etched using the resist as a pattern. After patterning the DARC layer and the underlying layer, both the resist and DARC layers are typically removed. The resist is removed using an ash step comprising exposure of the resist to an oxygen plasma, then DARC layer is removed, typically using a wet etch but also in some processes using a dry etch.
One problem which can result from the use of DARC layers occurs from the removal of the layer. The DARC layer is typically exposed to a wet etch of SuperQ (3% phosphoric acid, H3PO4, 37% ammonium fluoride, NH4F) or QEtch II (1% H3PO4, 39% NH4F). This wet etch also enters the opening in the underlying layer, and may etch this layer and expand the opening in the underlying layer beyond that etched with the photoresist pattern. This expansion may also occur if the DARC layer is removed with a dry etch. In many device designs this will undesirably expose another conductive feature, which may lead to shorting when the opening is filled with a conductive layer which contacts the exposed feature. This is especially true as semiconductor engineers design devices with tight critical dimensions (CD's) to maximize feature density. This may result in an unreliable device or a nonfunctional device, thereby decreasing yields and increasing costs. While the DARC layer is nonconductive, leaving it in place can contribute to device leakage.
A process which results in the aforementioned shorting of device features is depicted in
After forming the
After etching the digit line contact opening 40, resist layer 38 is removed, for example using an ash step (i.e. exposing the layer to an oxygen plasma) followed by a clean using a dilute solution of hydrogen peroxide (H2O2) and sulfuric acid (H2SO4) to remove any remaining residue to result in the
A new method and structure which reduces or eliminates the problems resulting from removing an antireflective layer with a wet or dry etch would be desirable.
An embodiment of the present invention provides a new method which, among other advantages, reduces problems associated with the manufacture of semiconductor devices, particularly problems resulting from the removal of a deposited antireflective coating (DARC) with a wet or dry etch.
In accordance with one embodiment of the invention a layer of boron-doped amorphous carbon (herein “a-C:B”) is used as a DARC layer. This a-C:B layer as a DARC layer, in contrast to conventional DARC layers, has the advantage of being removable through an ashing process, similar to that used for removal of photoresist. One advantage is that the DARC layer can be removed without a wet etch, and it may be removed simultaneously with the removal of an overlying photoresist layer.
Additional advantages will become apparent to those skilled in the art from the following detailed description read in conjunction with the appended claims and the drawings attached hereto.
It should be emphasized that the drawings herein may not be to exact scale and are schematic representations. The drawings are not intended to portray the specific parameters, materials, particular uses, or the structural details of the invention, which can be determined by one of skill in the art by examination of the information herein.
The term “wafer” is to be understood as a semiconductor-based material including silicon, silicon-on-insulator (SOI) or silicon-on-sapphire (SOS) technology, doped and undoped semiconductors, epitaxial layers of silicon supported by a base semiconductor foundation, and other semiconductor structures. Furthermore, when reference is made to a “wafer” in the following description, previous process steps may have been utilized to form regions or junctions in or over the base semiconductor structure or foundation. Additionally, when reference is made to a “substrate assembly” in the following description, the substrate assembly may include a wafer with layers including dielectrics and conductors, and features such as transistors, formed thereover, depending on the particular stage of processing. In addition, the semiconductor need not be silicon-based, but could be based on silicon-germanium, silicon-on-insulator, silicon-on-sapphire, germanium, or gallium arsenide, among others. Further, in the discussion and claims herein, the term “on” used with respect to two layers, one “on” the other, means at least some contact between the layers, while “over” means the layers are in close proximity, but possibly with one or more additional intervening layers such that contact is possible but not required. Neither “on” nor “over” implies any directionality as used herein.
A process for forming a semiconductor device using an inventive dielectric antireflective coating (DARC) is depicted in
Antireflective coating 60 in this embodiment is manufactured from amorphous carbon doped with boron to a concentration of between about 0.1 atom % to about 10 atom %, and up to a maximum of about 20 atom %. An a-C:B film with about 10 atom % of boron has an “n” value of about 1.80 and a “k” value of about 0.51 with reference to a 248 nanometer wavelength light. The “n” and “k” values can be tuned to desired levels by varying the concentration of boron in the a-C:B layer. Boron-doped amorphous carbon (a-C:B) can be removed with an oxygen plasma ash step similar to that of photoresist, and may be removed during the removal of any photoresist remaining after etching the underlying layer, as will be discussed below.
The a-C:B layer 60 of
Summary of Variable Ranges to Form a
Boron-Doped Amorphous Carbon Layer
in an Applied Materials ® Centura ® Etch Chamber
200° C.-450° C.
350° C.-400° C.
C3H6 flow rate
200 sccm-1,000 sccm
400 sccm-700 sccm
B2H6 flow rate
100 sccm-2,000 sccm
400 sccm-1,300 sccm
He flow rate
0 sccm-1,000 sccm
0 sccm-600 sccm
300 W-1,000 W
450 W-700 W
3.0 T-7.0 T
4.0 T-6.0 T
2,500 Å/min-6,000 Å/min
4,000 Å/min-5,500 Å/min
The deposition process above dopes the amorphous carbon with boron to between about 0.1 atom percent (atom %) and about 20 atom %, more preferably to between about 1 atom % and about 15 atom %, and most preferably to between about 5 atom % and about 10 atom %, depending on the B2H6 flow rate relative to the flow rates of the propylene and (if used) helium. With benefit of the present description, alteration of the gas flow rates to result in the desired boron atom % can be accomplished by one of ordinary skill in the art.
As the atom % of boron increases, the film becomes more opaque. An atom % of greater than about 20% is not considered preferable for most uses, because as the boron concentration increases, it becomes more difficult to sufficiently etch the layer with an oxygen plasma in a process described below to form an opening in the ARC layer. With no boron doping in the amorphous carbon, the DARC layer will react with the photoresist to form a resist footing, and thus the resist layer cannot be formed directly on an amorphous carbon layer with no boron doping. Thus it is preferable to dope the amorphous carbon layer with boron to between about 0.1 atom % and about 20 atom %.
After formation of the
After forming the structure of
During the ash of the a-C:B layer, adding fluorine to the oxygen plasma will increase the removal rate of the a-C:B layer. Thus it may be advantageous in some processes to expose at least the a-C:B layer to a fluorine-containing oxygen plasma. Fluorine may be introduced by the inclusion of a gas such as CF4, NF3, CH2F2 or CHF3 into the oxygen plasma during the ashing.
The embodiments described above allow for an improved removal of an antireflective coating through the use of a material (a-C:B) which can be ashed along with the photoresist layer rather than requiring removal through the use of an acid or a dry etch which can damage BPSG, TEOS, or other dielectric.
As depicted in
The process and structure described herein can be used to manufacture a number of different structures which comprise a structure formed using a photolithographic process.
While this invention has been described with reference to illustrative embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as additional embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. While the description above describes the use of the a-C:B layer as a DARC layer during the formation of a digit line contact opening, the inventive DARC layer can be used in many processes, for example during the etch of a dielectric to define capacitor bottom plates, during an etch to define the word lines, or during any patterning etch with which an antireflective layer is useful. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.
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|U.S. Classification||438/689, 438/636, 257/E21.257, 438/710, 257/E21.018, 257/E27.087, 257/E21.577, 257/E21.035, 257/E21.648, 257/E21.658, 438/711, 257/E21.029, 257/E21.253|
|International Classification||H01L21/8242, H01L21/033, H01L21/311, H01L27/108, H01L21/768, H01L21/02, H01L21/027|
|Cooperative Classification||H01L21/76802, H01L27/10852, H01L21/0276, H01L21/0332, H01L27/10888, H01L27/10811, H01L21/31122, H01L21/31144, H01L28/90|
|European Classification||H01L27/108M4D4, H01L21/311D, H01L21/311B2B2, H01L21/027B6B4, H01L21/033D, H01L21/768B2|
|Sep 24, 2003||AS||Assignment|
Owner name: MICRON TECHNOLOGY, INC., IDAHO
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